Embodiments of the present invention are directed generally to cable network fault isolation and more specifically to the isolation of faults in devices comprising the cable plant.
Cable networks deliver voice, data, and video to subscribers over a complex web of hubs, nodes, amplifiers, line extenders, and passive devices. Network management practices typically include device numbering systems to facilitate network topographical management. Device numbering systems are hierarchical thereby mimicking the trunk/cascade structure of the network itself. A well-implemented numbering system provides information about the physical location of a particular device within a network and the other devices to which the particular device connects.
Device numbering systems are generally designed to identify a device within a network to a level within the network deemed useful for network management. That is, a numbering system is used to manage network traffic, schedule maintenance, identify available capacity, balance loads among devices, and other important tasks. However, such a device numbering system is not able to isolate network problems to a device or cascade level.
FIG. 1 illustrates a typical cable system architecture. A headend 100 communicates with hub 105. Hub 105 comprises a cable modem termination system and switching/routing components. Hub 105 communicates with nodes 120A, 120B, 120. Nodes 120 provide an interface between the fiber-based transport medium of the cable network (between the headend 100 and upstream side of nodes 120) and the coax-based medium (between the downstream side of nodes 120 and the subscriber interface 145). The downstream side of node 120B is further illustrated as connecting to bridger amplifier 1 125 which in turn is connected to bridger amplifier 2 130. The serial path from node 120B through bridger amplifier 1 125 to bridger amplifer 2 130 is referred to as a cascade relative to node 120B. Bridger amplifier 1 125 has three branches that are cascades relative to bridger amplifier 1 125 and sub-cascades relative to node 120B.
As will be appreciated by those skilled in the art, FIG. 1 is a greatly simplified schematic of a cable network architecture. A hub typically serves 20,000 subscribers. A typical hub support from 100 nodes with each node capable of serving 2000 subscribers. In order to maintain signal quality and quality of service commitments, trunk amplifiers maintain high signal quality. Internal bridger modules in the trunk amplifiers boost signals for delivery to subscribers' homes. Line Extender amplifiers maintain the high signal levels in cascade after the trunk amplifiers, through the neighborhoods. Taps divide out small amounts of signal for connection to the homes. They typically have 2, 4 or 8 ports for connection of drop cables. Nominal cascade limits are up to 4 trunk amplifiers followed by up to 3 line extenders, with more in very rural areas. In suburban areas, cascades typically comprise 2 trunk and 2 line extenders. Because branching is unlimited, the total device count per node may be large despite short cascades.
Because of the number of devices in a cable network, identifying the cause of an outage can be a daunting problem. Cable network troubleshooting is often time consuming and craft/skill dependant in a sequence of staff positions. Customer service must interpret and correlate customer complaints, dispatch must efficiently contact and direct the maintenance crew, and the maintenance crew must efficiently troubleshoot a geographically dispersed system.
What is needed is a means for automating the process of isolating faults in a cable network that does not require re-engineering of the network or replacement of existing equipment.